Die pulsradiolyse einfacher merkaptane in luft freier wässriger lösung

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

The effect of pH and complexation on redox reactions between RS• radicals and flavins

Ahmad¹

1984

“…It is simpler than cysteine in that ionisation of the -SH group is the only process which leads to changes in net charge of the molecule with pH. The pKi and the magnitude of K, are known to be 10.0 and 1.8 X 10"-' , respectively (14,15). The disulphydryl lipoamide L(SH), was also used.…”

Section: Introductionmentioning

confidence: 99%

The dependence of the photochemically induced reduction of lumiflavin on pH, light intensity, and concentration of sulphydryl compounds

Surdhar¹

1985

Can. J. Chem. 63, 341 1 (1985). The spectral changes which occur on photolysis of flavin solutions containing P-mercaptoethanol (RSH) and lipoamide (L(SH),) are in accord with the formation of dihydroflavin, except at pH values below 3 for RSH. Here an oxygen-stable product is formed, which has X , , , 360 nm and is probably a C-4a substituted dihydroflavin. ' The fraction of flavin present when FlH2 reaches a photostationary state f(F1H2),, is dependent on pH and on the absorbed light intensity I,. At certain pH values the actual photostationary concentration of FlH2 is linear in the concentration of RSH, but for the lipoamide system shows a more complex dependence on concentration. The initial quantum yields are independent of absorbed light intensity in the pH range 7 to 10 for RSH, and increase strongly with pH in the region 7 to 9 for both sulphydryl compounds. In the pH range 5-6 they are linear in sulphydryl concentration. For RSH the results can be explained by a mechanism in which flavin triplet abstracts a hydrogen atom from RSH to form RS. and .FIH radicals, These radicals undergo back reaction to RSH and F1 or form RSSR and FlH2 by one of two mechanisms: (a) formation of RSSR--. which electron transfers to F1 or .FIH or (b) reaction of RS. with .FIH--RSH complexes. The results with L(SH), can be explained similarly. PARMINDER S. SURDHAR et DAVID A. ARMSTRONG. Can. J. Chem. 63, 34 1 1 (1 985). Les changements spectraux qui se produisent lors de la photolyse de solutions de flavines contenant du P-mercaptoCthano1 (RSH) et de la lipoamide (L(SH),) pourraient Ctre expliques par la formation de la dihydroflavine, i I'exception des pH inftrieurs i 3 dans le cas du RSH. Dans ces cas, il y a formation d'un produit qui est stable vis-i-vis de I'oxygtne, qui prtsente un X, , , , i 360 nm et qui est probablement une dihydroflavine substitute en position C-4a. La fraction de flavine qui est prtsente quand la FIH, atteint un Ctat photostationnaire, f(FIH,),,, qui depend du pH et de l'intensitk de la Lumikre absorbte, I,. A certains pH, la concentration photostationnaire reelle de la FlH, varie d'une f a~o n lintaire avec la concentration en RSH; dans le cas du systtme de la lipoamide, on note toutefois une relation plus complexe avec la concentration. Dans le cas du systtme du RSH et i d e s pH allant de 7 a 10, les rendements quantiques initiaux ne dkpendent pas de I'intensitk de la lumikre absorbCe; toutefois, pour chacun des composes sulfurCs et i des pH allant de 7 2 9, ces rendements augmentent rapidement. Aux pH allant de 5 i 6, ils sont IinCaires avec les concentrations en sulfhydryles. Pour le systkme RSH, les rtsultats peuvent Ctre expliquCs par un mecanisme dans lequel 1'Ctat triplet d'une flavine enlkve une hydrogtne du RSH pour former des radicaux RS et . FIH.Ces radicaux subissent des reactions de retpur vers le RSH et la F1 ou ils forment du RSSR et de la FIH, par I'un des deux mtcanismes suivants: (a) formation de RSSR-qui donne des reactions de transferts d'electron conduisant i la F1 ou au .FIH ...

“…The effect of radiation or of photolytic absorption on the pure mercaptans has been extensively studied in the gaseous state (11,12), in the solid polycrystalline state (13,14), and in single crystals such as cysteine (15,16). The metastable intermediates of chemical oxidation in dilute aqueous solutions have also been studied using fast flow techniques (17,18), flash photolysis (19), or pulse radiolysis methods (20), but until recently not much work had been done on the radiolysis and photolysis of thlols in dilute rigid solutions using inert or chemically indifferent organic matrices. We wish to report on some of the work done in this direction Can.…”

Section: Introductionmentioning

confidence: 99%

The Photolysis and Radiolysis of Simple Mercaptans in Dilute Glassy Matrices

Skelton¹,

Adam²

1971

The e.p.r. spectrum of thiyl radicals is obtained when dilute solutions of aliphatic mercaptans are photolyzed in a xenon matrix at 77 OK. No proton hyperfine structure is observed at low concentrations of thiol but it appears at higher concentrations due to the reaction of hot hydrogen atoms with solute mercaptan molecules. When small amounts of the thiols are dissolved in glassy hydrocarbon matrices such as 3-methylpentane, there is produced after photolysis hyperfine structure characteristic of the solvent as well as the thiyl resonance. The e.s.r. absorption due to the solvent species disappears when the matrix is warmed a few degrees above 77 "K but thiyl radicals are stable up to the melting point of the glass. The corresponding y-irradiated glasses do not give thiyl absorption, but two other species are produced along with solvent radicals. No thiyl radicals are observed following radiolysis, or upon photobleaching the new species. The spatial distribution of the neutral radicals in the glasses is discussed in view of these results.Le spectre de r.p.e. de radicaux thiyl est obtenu lors de la photolyse de solutions dilukes de mercaptans aliphatiques dans une matrice de xenon a 77 OK. On n'observe pas la structure hyperfine du proton en utilisant de faibles concentrations de thiol, mais elle apparait lorsqu'on utilise des concentrations plus ClevCes a cause de la reaction des atomes d'hydrogkne chauds avec les molCcules de mercaptan en solution. Si on dissout de petites quantites de thiol dans des matrices d'hydrocarbure vitreuses, tel le methylpentane-3, il se produit apres photolyse, une structure hyperfine qui est caracteristique du solvant aussi bien que de la resonance du thiyl. L'absorption r.p.e. due a l'espece solvant disparait quand la matrice est chauffee a quelques degris au-dessus de 77 OK, mais les radicaux thiyl demeurent stables jusqu'au point de fusion du verre. Les verres irradits aux rayons-y ne donnent pas d'absorption thiyl, mais deux autres especes sont produites en meme temps que les radicaux de solvant. On n'observe pas de radicaux thiyl apres radiolyse, ou pendant la photodCcoloration des nouvelles espkces. On discute de la distribution spatiale des radicaux neutres dans les verres pour arriver aces rksultats.